SideBySide2: Scroll to first diff chunk when opening view

If the first diff chunk is not within the visible region, scroll
to make it visible in the middle of the editor. When a large file
is opened with context set to whole file this saves a lot of time
trying to get to that first edit.

Change-Id: Ie659ecddc03bc9a5b81d2ffcc4175424a9cddcca
1 file changed